A seat belt system for restraining a vehicle occupant typically includes seat belt webbing, a seat belt locking tongue on the webbing, and a seat belt buckle. The tongue on the webbing is inserted in the buckle when the webbing has been placed about a vehicle occupant. A latch mechanism in the buckle interlocks with the tongue to secure the webbing about the occupant. Such a seat belt system may also include a buckle switch for indicating whether or not the tongue is locked in the buckle.